Currently, there exist ground velocity detection apparatuses to be installed on a moving object such as a vehicle, for measuring a velocity of the moving object relative to a ground surface, e.g., the inventions disclosed in Patent Literatures 1 and 2.
The invention disclosed in Patent Literature 1 is provided with: a transmitter for generating a radio wave; an antenna for emitting the radio wave from a vehicle to a track surface; a mixer for mixing reflected power from the track surface with a part of transmitting power to obtain a Doppler signal component; and a pulse generator and a counter for detecting a signal at a certain level or more from the mixer's output and converting the signal into a pulse. The invention is configured to obtain a travel distance and a required time by measuring a number of pulses as well as start and end times of the pulses, and to derive a velocity of the vehicle from the travel distance and the required time.
The invention disclosed in Patent Literature 2 is provided with: a first ground distance sensor for measuring a distance to a ground surface; a second ground distance sensor separated from the first ground distance sensor by a predetermined distance in a traveling direction of a vehicle, the second ground distance sensor measuring a distance to the ground surface at a point remote from the first ground distance sensor by a predetermined distance; first ground surface tracing means for tracing a ground surface on which a vehicle travels, based on a distance signal from the first ground distance sensor; second ground surface tracing means for tracing the ground surface on which the vehicle travels, based on a distance signal from the second ground distance sensor; time delay detecting means for comparing a feature of the ground surface traced by the first ground surface tracing means with a feature of the ground surface traced by the second ground surface tracing means, and detecting a time difference when the first ground distance sensor passes a point and when the second ground distance sensor passes the point; and ground velocity detecting means for detecting a ground velocity of the vehicle from the time difference detected by the time delay detecting means and the distance between the first ground distance sensor and the second ground distance sensor.
Using the measured velocity, it is possible to calculate a travel distance from a predetermined reference point, or a total travel distance.